public class test {
    public static void main1(String[] args) {
        String str = "abc";
        str += "def";

        System.out.println(str);
    }

    public static void main2(String[] args) {
        String str = "hello";
        StringBuilder stringBuilder = new StringBuilder();
        stringBuilder.append(str);
        stringBuilder.append("abc");
        str = stringBuilder.toString();
        System.out.println(str);
    }

    public static void main3(String[] args) {
        int[] arr = new int[100];

        StringBuilder stringBuilder = new StringBuilder("hello");

        stringBuilder.reverse();
        System.out.println(stringBuilder);
    }

    public static void main4(String[] args) {
        String s = "hello,H";

        s = s.toLowerCase();
        System.out.println(s);
    }

    public static void main(String[] args) {
        
    }
}
